Rhynchosaurs Fossil range: Early Triassic–Late Triassic PreЄ Є O S D C P T J K Pg N
life restoration of Hyperodapedon
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Sauropsida
Subclass:	Diapsida
Infraclass:	Archosauromorpha
Order:	Rhynchosauria Osborn, 1903
Family:	Rhynchosauridae Huxley, 1859
Genera
Mesosuchus Fodonyx Howesia Stenaulorhynchys Rhynchosaurus Otischalia Isalorhynchus Hyperodapedon Paradapedon

Rhynchosaurs were a group of Triassic diapsid reptiles related to the archosaurs. They were herbivores, and at times abundant (in some fossil localities accounting for 40 to 60% of specimens found), with stocky bodies and a powerful beak.

Skull of Rhynchosaurus articeps

Paradapedon from Late Triassic of India

Early primitive forms like Mesosuchus and Howesia were more typically lizard-like in build, and had skulls rather similar to the early diapsid Younginia, except for the beak and a few other features.

In later and more advanced genera the skull is short, broad, and triangular, becoming much wider than long in the most advanced forms like Hyperodapedon (= Scaphonyx), with a deep cheek region, and the premaxilla extending outwards and downwards to form the upper beak. The broad skull would have accommodated powerful jaw muscles. The lower jaw was also deep, and when the mouth was closed it clamped firmly into the maxilla (upper jaw), like the blade of a penknife closing into its handle. This scissors-like action would have enabled rhynchosaurs to cut up tough plant material.

The teeth were unusual, those in the maxilla and palate modified into broad tooth plates.

The hind feet were equipped with massive claws, presumably for digging up roots and tubers by backwards scratching of the hind limbs.

Like many animals of this time they had a worldwide distribution, being found across Pangea

These abundant animals died out suddenly at the end of the Carnian (Middle of the Late Triassic period), perhaps as a result of the extinction of the Dicrodium flora on which they may have fed.

[edit] See also

• Paleorrota

[edit] External links

• Dinosaurs of Rio grande do Sul.

[edit] References

• Benton, M. J. (2000), Vertebrate Paleontology, 2nd ed. Blackwell Science Ltd
• Carroll, R. L. (1988), Vertebrate Paleontology and Evolution, W.H. Freeman & Co.
• Dilkes, D. W. 1998. The Early Triassic rhynchosaur Mesosuchus browni and the interrelationships of basal archosauromorph reptiles. Philosophical Transactions of the Royal Society of London: Biological Sciences, 353:501-541.

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